1. Field of the Invention
This invention relates to deriving power from solar sources.
2. Brief Description of Prior Art
U.S. Pat. No. 5,300,817 is one prior art attempt to collect solar power using a chimney effect. The housing of the device is constructed partially of glass such that air heated by the sun rises within a chimney. As the air rises in the chimney it can drive a turbine. A problem with the prior art is that these large solar collectors are expensive to build and must take up a large section of land. Therefore it is important to derive the maximum amount of energy from as compact and economical structure as possible, power interruption is also an important consideration. It is also important that a solar generator be able to produce energy in a range of conditions that might include cloudy days, sunny days and days that fluctuate between cloudy and sunny. Often times the prior art requires an expensive buffer such as a battery bank to even out energy flow between sunny and cloudy days, or a thermal storage such as a molten salt tank to even out the energy flow during intermittent cloudiness within a day.
In prior art pure solar thermal chimney towers such as U.S. Pat. No. 5,300,817, all electrical power generation is derived from the mass flow and the pressure differential of the updraft to drive a wind turbine and electrical generator. For a given electrical power generation rate, the diameter of a pure solar thermal chimney tower structure needs to be large to allow for adequate volume of air flow. The pure solar thermal chimney tower structure needs to be high enough to generate adequate buoyancy (pressure differential) in the updraft. The diameter of the flared portion of the pure solar chimney also needs to be large to collect enough solar energy to heat up a large volume of air to generate adequate amount of updraft. Thus a large tall structure is required and the cost of construction makes the arrangement impractical.
It is also known to use a field of heliostats (solar mirrors) to focus solar energy. When the solar input into the solar thermal receiver fluctuates such as from temporary misalignment of heliostats (control or mechanical glitches), or intermittent cloudiness, or rapidly varying grid electrical power demand, a single spool (mechanically coupled compressor and turbine) pure solar Brayton cycle is susceptible to turbine instability or receiver burnout. Thus heliostat arrangements typically require special safety consideration to avoid damaging equipment with the intense focused solar energy. As a result, in practice, heliostats are often taken off line, generating no energy, when conditions are less than optimal. This make many prior art arrangements either expensive to operate or unreliable. Heliostats have to be situated at certain minimum distances from the central receiving tower to prevent the reflected sun rays striking the solar receiver at unfavorable angles, and to avoid the shadow cast by the central receiving tower. The land area adjacent to the central receiving tower in a heliostat field is thus wasted.
Prior art arrangements have failed to be able to provide enough energy benefit to offset the cost of the land used and the structure required.